Strand chuck



Nov. 18, 1969 w. DROUILLARD 3,478,396

STRAND CHUCK Filed Jan. 4, 1968 I INVENTOR.

51 52:; 5 WILLIAM DROUILLARD United States Patent Int. Cl. F16g 11/04 US. Cl. 24-126 3 Claims ABSTRACT OF THE DISCLOSURE A tubular body is provided with a conical bore which receives a set of tendon engaging jaws. The body threaded and a threaded collar or bushing is engaged therewith. A tendon which extends through a concrete structure extends through the body and is engaged by the jaws. The tendon is stressed and the device moved along the strand into engagement with the concrete form around the tendon. The tension may then be released and the tendon severed. With tension applied to the tendon and jaws fully engaged with the tendon, rotation of the threaded collar or bushing with respect to the body may be used to cause the rotating part to bear against the structure so that when the external tensioning device is released no loss in strain occurs in the tendon.

This invention relates to improvements in strand chuck devices used most commonly in the prestressed concrete field of the construction industry, and particularly to the type which are used for pre-tensioning and post-tensioning of concrete structures by providing for an adjustable movement of the chuck body away from the concrete structure to maintain without loss, the full tension in a tendon extending through or into the structure.

The primary improvement is embodied in the addition of an adjustable forward extension of the chuck body by means of a threaded collar or bushing. In application with the tendon stressed to the desired initial tension and the jaws fully engaged with the tendon, the collar or bushing is adjusted forward to engage or seat against the bearing plate or concrete form. When the stress is subsequently released from the ram or jacking device, no loss in stress or strain occurs in the tendon.

Briefly, the invention contemplates a chuck body which carries tendon gripping jaws through and between which the tendon extends. The exterior of the body is threaded and a collar or sleeve is disposed thereon which may be turned to cause the sleeve to engage a bearing plate on the concrete structure to locate the body outward from the structure and maintain the full tension on the tendon which is gripped by the jaws. Alternatively, the interior of the body may be threaded at one end and a hollow bushing threaded in that end which, when screwed outwardly of the body, will move the body away from the concrete structure. One end of the collar or bushing may be of spherical formation and engaged in a complementary socket in the bearing plate to provide automatic alignment.

Among the advantages which accrue from the use of the above device may be included the fact that they provide an easy, accurate and positive means for internal compensation of stress and strain losses which are particularly critical with the use of short tendons.

It is apparent then that use of this improved device eliminates the losses of tension or stress inherent with presently used strand chucks which losses are caused by the seating of the jaws into the tapered bore of the chuck body.

In addition, it is seen that this improved device in conjunction with a suitable hydraulic jack provides a 34l78396 Patented Nov. 18, 1969 'ice I means by which stress or strain in a tendon may be easily corrected or adjusted after an initial tensioning.

In the drawings: 1

J FIG. 1 is an exploded view of the strand chuck;

FIG. 2 is an elevational view of the chuck disposed on a tendon ready for tensioning;

FIG. 3 is a view similar to FIG. 2 after the tendon is tensioned;

FIG. 4 is a view showing the final stage of its use;

FIG. 5 is a fragmentary elevational view of the chucks in use for holding a pretensioned, precast beam in place on a column;

FIG. 6 is an exploded view of another embodiment of the invention;

FIG. 7 is an exploded view of another embodiment of the invention as used with the chuck of FIGS. 1 through 4; and

FIG. 8 is a similar view of the invention of FIG. 7 used in conjunction with that of FIG. 6.

Referring to the drawings throughout which like parts have been designated by like reference characters and more specifically as best shown in FIG. 1, the strand chuck includes a cylindrical body 10 having a tapered bore 12 and a threaded exterior 14. Jaws 16 are provided for seating in the bore 12, their exterior being complementary to the surface of the bore and having semi-cylindrical gripping surfaces or seats 18 for engagement with a tendon. The seats 18 may have surfaces which are smooth, corrugated, knurled or otherwise formed to provide a good gripping surface with a tendon. Three jaws are shown but two or more could be used. The seat 12 in the body is so proportioned relative to the jaws 16 that the jaws ends do not bottom in the inner end of the seat. The jaws are sufliciently long that when seated they preferably project beyond the end of the body.

A collar 20 is provided having threads on its interior for threaded engagement with the threads 14 on the body 10. The exterior of the collar may be knurled or provided with flats or notches for engagement by hand or a suitable wrench. Although the collar is illustrated as being shorter than the body, it is contemplated that the length could be longer than shown or even longer than the body, if desired.

One manner in which the device may be used is shown in FIGS. 2 through 4, wherein a tendon T is shown projecting through a bearing plate B or form. which helps define a concrete structure C which is to be prestressed, it being assumed that the tendon passes through the concrete and is similarly secured on the far side as is well known in the art. The body 10 with the sleeve or collar 20 is passed over the tendon, after which the tendon is stressed by a suitable jack or come-along. With the end of the body 10 against the bearing plate, the jaws-18 may now be inserted and forced into gripping engagement with the tendon. It will be appreciated that the complete assembly of the chuck with the tendon may be elfected prior to placing the ultimate desired tension on the tendon.

FIG. 3 shows the device where the tendon has been tensioned to the desired amount of tension which may be accurately determined by the tensioning device. The body 10 has now moved away from the bearing plate B, The user now has two choices of. procedure; in the first, the collar is now rotated on the body into engagement with the bearing plate where it can be tightened snugly against the bearing plate by hand or a Wrench to the position shown in FIG. 4. The tension on the tendon beyond the body may now be relieved. The loss of tension or strain loss on the tendon due to the seating of the jaws in the body and on the tendon may be compensated for by externally retensioning and further tightening of the collar against the bearing plate. The alternative procedure, after the tension has been applied as shown in FIG. 3, by means of the coupling D, is to rotate the collar to the left until it is in contact with the bearing plate, as shown in FIG. 4. In this instance, full tensioning and jaw seating are accomplished at once.

One advantage of the improved chuck resides in the fact that the tendon tensioning device may be connected directly to the body by providing coupling means D, shown in dotted lines in FIG. 3, which may be threaded directly on the end portion of the body. This results in a savings in time required to tension a tendon as well as a savings in tendon length which can become significant when tendons are short.

The device may be used to make connections as for securing pretensioned, precast beams to columns. In this instance, the tendons used to pretension one member may be used as connecting tendons with material savings. As shown in FIG. 5, the column 22 is shown with a step or seat 24 upon which a beam 28 may be placed with the tendons T projecting through holes 26 formed in the columns. Here the bearing plates B engage with the outward surface of the column and the collar 20 is shown on the body with the jaws 16 engaging the tendon and the collar tightened against the bearing plate.

When the tendons have a center-to-center spacing so close together that interference between the chuck collars may occur, a modified form of the invention, illustrated in FIG. 6, may be used. In this instance, the body 30 is longer and is provided with a threaded bore 32 at one end which is connected by a bore 34 of reduced diameter to the jaw seat 36. The jaws 18 may be seated in the seat 36 in a manner as described although it is contemplated that an additional cap 38 may be used having a stem 38a which extends into the bore 40 to engage with the jaws or spring to tighten the same, as shown in Patent No. 3,048,775. In this instance, the tension controlling means comprises a bushing having a threaded stem 42 and a hexagonal or knurled head 42a that is threaded into the bore 32. After assembly with the tendon, the bushing may be turned to move it outwardly of the bore against the usual bearing plate to maintain full tension on the tendon. Likewise, as described in conjunction with FIG. 3, an interiorly threaded coupling device may be used to connect the body directly to the tensioning device by threading the coupling into the threads 40.

Another improvement, as shown in FIGS. 7 and 8, contemplates providing the bearing plate 50 with a seat 52 of spherical radii and the collar or sleeve 54 with an end portion 54a which is complementary to the seat 52. Thus the collar 54 can move on the surface 52 and provide a self-aligning feature which is an advantage.

Likewise, as shown in FIG. 8, the bushing type of adjustment member may be provided with a similar end face 420 for the same purpose.

It is apparent that the device is particularly useful in conjunction with short length tendons such as are used in making railroad ties. Tensioning directly on the body 10 as shown in FIG. 3 will be seen to result in a reduction in the percentage of tendon material scrap.

Having thus described the invention in some embodiments thereof it will be appreciated that numerous and extensive departures may be made thereof without departing from the scope of the invention.

I claim:

1. A strand chuck for gripping and tensioning a tendon extending from the exterior of a structure including a body having an internally tapered bore and tendon engaging jaws disposed in said bore and arranged to tighten upon the tendon when tension is applied thereto, the improvement which comprises threads for said body and structure engaging threaded means in threaded engagement with said threaded part of the body and arranged to engage said structure and position said body with the tendon away from the structure when said last threaded means is rotated relative to the body, said body and jaws being so formed that the tendon may extend beyond said body and pretensioning applied thereto and said chuck slipped on the tendon into proximity with said structure, said body being interiorly threaded at one end, a hollow threaded bushing disposed in the end, and said bushing having an arcuate end for self alignably supporting said structure.

2. A device as described in claim 1 wherein said threaded bushing is provided with a curved semi-spherical end and a bearing plate is provided having one side for engagement with said structure and a seat complementary to said spherical surface on the threaded means is provided for the threaded means.

3. A device as described in claim 1 wherein said body is interiorly threaded at :both ends and means is provided for connecting the device to strand tensioning means.

References Cited UNITED STATES PATENTS 2,041,385 5/1936 Van Laanen.

2,320,543 6/1943 Doughty.

2,511,761 6/1950 Barber 24--136X 3,049,368 8/1962 Jansen 2s7 20.3 3,309,744 3/1967 Sironi 24 122.6

FOREIGN PATENTS 516,382 1/1953 Belgium.

1,209,949 4/1960 France.

739,480 10/1955 Great Britain.

BERNARD A. GELAK, Primary Examiner US. Cl. X.R. 

